This invention relates generally to power distribution and, in particular, to a module capable of receiving a power related command by way of a communications interface and routing power from an input to one of a plurality of outputs in accordance with a command received. The module is particularly useful in vehicular applications, where it may be interfaced to an existing network to simplify interconnections and eliminate wiring.
Vehicles such as automobiles have traditionally routed electrical power from a source such as a fuse block or breaker panel to control energy consuming loads via modules including switches and/or relays. Generally the fuses for breaker panel is conveniently located either under the dashboard or in the engine compartment. Many of the controls are located on the dashboard, especially on the driver""s side. Other controls may be located closer to their associated loads, as with door-related or seat-related devices.
With today""s automotive technology, including complex safety features, climate control and operational devices, extremely complex wiring harnesses have resulted. Over the past 15 years, various approaches have been taken to reduce the number of wires and cables, thereby simplifying the manufacturing process, including lead dress requirements. Reducing the number of higher power cables in favor of low power signal lines adds a further advantage of reducing vehicle weight.
One way to limit the number of high power cables and to reduce the amount of wiring in general is to utilize multiplexing systems whereby control signals are exchanged among switching units and loads distributed throughout the vehicle, instead of having a separate power line for each load radiating from the central fuse box or breaker panel.
An early multiplex system for a vehicle is described in U.S. Pat. No. 3,864,578. This system includes an encoder unit preferably disposed at the head of the vehicle""s steering column at or near the hub of the steering wheel which provides a timing signal and a code signal which are responsive to the position of operator actuable controls. A plurality of substantially identical decoders receive both the timing and code signals and provide a plurality of outputs driving relay means for selectively energizing vehicle components. This system improved on the existing prior art by offering a standby mode of operation wherein the decoder and encoder means draw no significant current and by warning an operator in case of failure of any controlled loads such as a brake lamp. However, this system is essentially synchronous in at a timing signal is delivered to all decoders with the code signal being interpreted with respect to this timing signal. As such, serious reliability problems could result from the use of this system in the event an incorrect synchronous signal were transmitted to all connected receivers. This system also requires that a plurality of high gain actuators, which together comprise the relay means, are connected in line with each load.
The system described in U.S. Pat. No. 4,156,151 provides an electrical energy distribution system for motor vehicles in which a single power line having an associated single control line can be used to feed a plurality of remote control units to which a plurality of current consumers are connected. A central control unit generates coded pulse signals for identifying the current-consuming load and means are provided for decoding signals received at a remote control unit associated with a group of selected power consumers. This system, however, is very complex and relies upon discrete components to monitor pulses contained in square waves in order to properly decode the address of a remote control unit. The system is therefore prone to error and difficult to expand, particularly if numerous analog controls are required.
A more recent vehicle multiplex system is disclosed in U.S. Pat. No. 4,845,708. In this system, both power buses and control buses radiate from the fuse block and the control buses interconnect a controller with numerous input and output units distributed about the vehicle. Preferably, the controller selects one of the control buses as an active bus at any given time and isolates the remaining control buses both from the active control bus and from the controller in order to improve system reliability and reduce electromagnetic interference. This system suffers from the need for multiple input and output circuits which are functionally different from one another. Also, as with all the prior art so far referenced, these input and output circuits are not intelligent enough to facilitate two-way communication over a sophisticated communication path, whether using a proprietary or standard protocol.
The present invention is a power distribution module, especially for vehicular applications, including an input/output port adapted for connection to an external multiplexed communication path. The module includes transceiver circuitry connected to the input/output port operative to send and receive messages over the communication path in digital form, and the module is flexible enough to support a standard or user-defined communication protocol.
The module further includes an input for connection to a source of power, a plurality of power output ports, and a plurality of controllable power switches, each associated with one of the power output ports, each power switch being operative to route power from the source of power to an associated power output port in accordance with a control signal. Control circuitry, operatively connected to the transceiver circuitry and to each power switch, facilitates the sending and receiving of messages over the communication path through the transceiver circuitry, and in accordance with a received message, provides a control signal to a specific power switch, causing power to be routed from the power source to the output port associated with that switch. Fault-detection circuitry is included to compare signals representative of messages being sent and received and provide a fault signal to the control circuitry in the event of contention between the messages being sent and received.
In a preferred embodiment, the module is entirely contained within an enclosure having an integral heat sink in thermal communication with the power switches. A power input connector is provided on the enclosure to receive incoming power from a source of power, and a plurality of power-output terminals are provided on the enclosure, each terminal being adapted for connection to a power-consuming load. The power switches preferably take the form of solid-state devices such as power MOSFET, including two-level charge-pump circuitry operative to boost the voltage provided to the gate of the MOSFET in order to deliver a desired, predetermined voltage through the associated power-output port yet conserve energy during quiescent periods.
The control circuitry may be implemented either as a general-purpose microcomputer or alternatively, as more dedicated circuitry for example, in the form of an application-specific integrated circuit or using programmable array logic. In the event that a microcomputer is used, the module may further include a timer reset circuit configured to receive a signal from the controller and reset the controller in the event that the signal is not received. For example, this circuit may include a low-frequency oscillator which continuously attempts to reset the controller unless an inhibit signal is supplied by the controller.
The module preferably further includes output protection circuitry operative to sense the current through a power switch and turn of the switch if the current through the switch exceeds a predetermined value. Circuitry capable of detecting open-load conditions or excess temperature may alternatively be provided. Voltage regulation circuitry may also be included to convert an incoming voltage into a voltage for use within the module, for example if the control circuitry is implemented with a microcomputer configured for a lower-voltage supply.